U.S. Pat. Nos. 5,656,883 and 4,663,559, both to Alton O. Christensen, Sr. (Christensen) disclose true-ohmic contact structures for injecting charge into a vacuum interface, namely, field emission. U.S. Pat. No. 5,977,718, U.S. patent application Ser. No. 08/281,912 and U.S. patent application Ser. No. 09/218,233, all to Christensen, disclose other materials of a true-ohmic contact interface to inorganic, organic and polymer devices. More specifically, U.S. patent application Ser. No. 09/218,233 discloses woven polymer semiconductors and electroluminescent fibers comprising pixel components and control circuitry. Furthermore, U.S. patent application Ser. No. 08/281,912 discloses true-ohmic contacts to inorganic and metal-organic materials.
The status of the prior art in electroluminescent (EL) polymer device design is well documented by the review article by R. H. Friend, et al., in “Electroluminescence in Conjugated Polymers,” NATURE, Vol. 397, Jan. 14, 1999, p 121. This article, hereafter referred to as “Friend”, is limited to conjugate polymer light emitting diode devices (LED's) having indium-tin oxide (ITO) as the hole-injecting contact. The reference is cited not only as background of the prior art, but also because specific needs for improvement in the prior art are discussed. These are summarized as follows by topic with applicable page, column and initial line number:
1. Low barrier contacts: (page 124, col. 2, line 17) Friend states that both hole-injecting and electron-injecting electrodes with relatively low barriers for charge injections are required so that high current densities and concomitant light emission are produced at low voltages.
2. Low mobility: (page 124, col. 2, line 12) Friend states that mobility is field (energy) dependent.
3. Space charge limitation: (page 124, col. 2, line 1) Friend states that current flow in LED's is not limited by injection, but bulk limited by build up of space charge from low carrier mobility.
4. Current balancing: (page 125, col. 1, line 5) Friend states that injection and transport of holes into the bulk of the polymer must be matched by injection and transport of electrons from the opposite electrode, and that the control of injection rates (by introducing heterojunctions) has been shown to be effective for obtaining charge balance.
5. Reduced radiative emission: (page 126, col. 1, line 25) Friend states that in device structures of the type discussed here, the presence of a metallic cathode (ITO) provides a mirror thereby reducing the emission rates.
6. Interchain interaction reduces radiative emission: (page 125, col. 2, line 38 and page 126, col. 1, line 3) Friend states that interchain interactions produce lower energy excited states not strongly radiative,
7. Need economic integrated pixel control circuitry; (Page 127, col. 1) Friend discusses needs for economically efficient means for producing integrated pixel control circuitry.
Improvements in these areas will be set forth in subsequent sections of this disclosure.